Method of forming and assembling a piston for a hydraulic damper

ABSTRACT

A piston and piston rod subassembly for use with a hydraulic damper is disclosed. The piston is formed from a substantially flat blank having a pattern of bendable tabs provided along a first edge. A bendable skirt is provided along a second edge of the blank. After the blank is formed into a cylindrical body, the tabs are crimped onto a flanged end of a piston rod. A valve assembly can be retained in the cylindrical body by crimping the skirt over the valve assembly.

This is a division of application Ser. No. 07/502,717 filed on Apr. 2,1990, now U.S. Pat. No. 5,038,897.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to hydraulic dampers forvehicles and, in particular, is concerned with a piston and piston rodsubassembly and a method of manufacture and assembly.

2. Description of the Related Art

A typical hydraulic shock absorber or strut includes a piston and pistonrod subassembly which reciprocates in an inner cylinder duringcompression and rebound of the damper. The piston may contain a valvingpackage to vary the flow of hydraulic fluid from first and secondchambers in the inner cylinder, resulting in desired dampingcharacteristics.

The piston is generally formed as a solid cylindrical member requiringseveral machining and cutting operations. An inner passage is boredthrough the piston to receive the valving package and permit the flow offluid. Oftentimes, the valving package is retained within the piston bya crimping procedure. A sealing band can be provided around the outercircumference of the piston to provide a seal against the inner surfaceof the inner cylinder. In other constructions, a piston can be formed byvarious elements into a substantially cylindrical package capable ofreciprocating in the inner cylinder.

In the majority of shock absorbers and struts, the piston is eithermounted on a threaded piston rod or welded to the piston rod. Drawbackscan occur with either one of these mounting techniques. Threading apiston rod increases manufacturing and assembly costs. Furthermore, thejoint between the piston and the rod can become loose during operation.An example of a threaded piston rod can be found in U.S. Pat. No.3,901,359.

While welding a piston to the rod may be less expensive than threadingthe rod, the heat generated by the welding process can distort thepiston and its concentricity. Lack of concentricity can cause a pistonto bind as the rod reciprocates in a damper, resulting in a defectiveunit. Second, weld spatter can become attached on and may adverselyaffect the valving, thereby interfering with fluid flow. Also, heat fromthe welding operation to attach the piston to the rod may damage thesealing band provided on the outer circumference of the piston. Anexample of a welded piston can be found in U.S. Pat. No. 3,724,615.

While conventional piston and piston rod subassemblies are successfullyutilized, the art continues to seek improvements. It is desirable toprovide a piston housing for containing a valving package which can beeconomically mounted on the piston rod without damaging the piston.Specifically, it is desirable to provide a piston and piston rodsubassembly without the expense of current threading operations and/orthe potentially adverse effects of welding.

SUMMARY OF THE INVENTION

The present invention includes a piston and piston rod subassembly for ahydraulic damper and a method of manufacturing the subassembly. Thepresent subassembly can be utilized with conventional shock absorbersand struts and can receive conventional piston valving elements. Thepiston is secured to the piston rod without a threading operation or awelding process.

In a preferred embodiment, the present invention includes a piston andpiston rod subassembly for use with a hydraulic damper. The piston isformed from a substantially flat blank having a pattern of bendable tabsprovided along a first edge. A bendable skirt is provided along a secondedge of the blank. After the blank is formed into a cylindrical body,the tabs are crimped onto a flanged end of a piston rod. A valveassembly can be retained in the cylindrical body by crimping the skirtover the valve assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of the present formedblank prior to striking and illustrating a first tab pattern.

FIG. 2 is a perspective view similar to FIG. 1 illustrating an alternatetab pattern on the formed blank.

FIG. 3 is an enlarged end view of the formed blank of FIG. 1.

FIG. 4 is a reduced edge or side view of the formed blank of FIG. 1.

FIG. 5 is a side view of the formed blank illustrating a first strike ina die progression.

FIG. 6 is a side view of the formed blank illustrating a second strikein the die progression.

FIG. 7 is a side view of the formed blank illustrating a third strike inthe die progression resulting in a cylindrical piston housing.

FIG. 8 is an exploded perspective view of the present piston and pistonrod subassembly illustrating the piston housing of FIG. 7 partiallyillustrated in section and a flanged piston rod.

FIG. 9 is a sectional view of the present piston and piston rodsubassembly mounted in a shock absorber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A substantially rectangular, formed blank indicated generally at 10 isillustrated in FIG. 1. The blank 10 can be formed from conventionalstrip stock and is cut to a finite length. The thickness and material ofthe blank 10 permit bending or deformation as described below.

As viewed in FIG. 1, the front or upper edge 12 of the blank 10 is cutin a pattern of long tabs 14 and short tabs 16. Each tab 14 and 16 isformed so as to be bendable. Preferably, each tab 14 and 16 can be bentapproximately perpendicular to the plane of the blank 10 as describedbelow.

The long and short tabs 14 and 16 can vary as desired. In particular,the lengths of the long tabs 14, as well as the lengths of the shorttabs 16, can differ in various embodiments of the blank 10. Furthermore,the distance between the tabs 14 and 16 can vary and the pattern of tabs14 and 16 can be varied. For example, in the embodiment of FIG. 1, apattern of three long tabs followed by a short tab 16 is repeated alongthe length of the upper edge 12. A rolling stock (not illustrated) ofthe pattern can be cut as desired between two adjacent long tabs 14 orbetween a long tab 14 and a short tab 16. In any pattern selected, thethickness and material of the tabs 14 and 16 permit bending ordeformation as described below.

In a second embodiment illustrated in FIG. 2, a blank 10A has a patternof one long tab 14A followed by two short tabs 16A. Note that thedistances between tabs 14A and 16A vary from similar elements in blank10. Other elements of blank 10A are similar to blank 10 and aredesignated with like reference numerals followed by the letter "A".Additional embodiments of the pattern of long and short tabs are easilyenvisioned. Also, a plurality of equally spaced tabs of a single heightcan be provided.

A rear or lower edge 18 of the blank 10 is provided with a skirt 20. Thethickness and material of the skirt 20 permit bending or deformation asdescribed below.

If desired, a plurality of ridges 22 can be provided on an outer surfaceof the blank 10. The ridges 22 are formed by any suitable means alongthe length of the blank 10 between the tabs 14 and 16 and the skirt 20.A valve seat 23 in the form of two steps is provided on an inner surfaceof the blank 10.

In FIG. 4, the blank 10 is turned on its upper edge 12 so that only thelower edge 18 and valve seat 23 are illustrated. FIGS. 5, 6 and 7illustrate successive steps of a forming process wherein the flat blank10 is formed into a cylindrical piston housing 24 (FIG. 7). In the firststrike of the process, the blank 10 is bent to form a U-shaped member26. The strike can be accomplished by any suitable means, including amale punch and a female die. After a second strike illustrated in FIG.6, the U-shaped member 26 is formed into a rounded member 28. Upon athird strike, a continuously round, cylindrical piston housing 24 isproduced. It is appreciated that the illustrative steps of FIGS. 5, 6and 7 can be combined, and that other methods may be used to form theblank 10 into the piston housing 24.

An unassembled piston and piston rod subassembly indicated generally at30 is partially illustrated in FIG. 8. The piston housing 24 is a hollowmember for receiving a piston rod 32 and a valve assembly 34 (FIG. 9).The piston rod 32 is formed with an annular flange 36 at its lower end.Preferably, the diameter of the flange 36 is slightly less than thesmallest inner diameter of the piston housing 24.

The tabs 14 and 16 are bent or crimped to retain the piston housing 24on the piston rod 32. First, the short tabs 16 are bent or crimpedinwardly to form a seat for a lower surface 38 of the flange 36. Second,the piston rod 32 is positioned so that the lower surface 38 of flange36 rests on bent short tabs 16 as illustrated in FIG. 9. Third, the longtabs 14 are bent or crimped inwardly over a top surface 40 of the flange36 to retain the piston housing 24 to the piston rod 32. It isappreciated that the short tabs 16 must be of a minimum height dependentupon the diameter of the flange 36 so that when bent inwardly theycollectively form a seat for the lower surface 38 of the flange 36.Also, the long tabs 14 must be a minimal height to extend over the topsurface 40 of the flange 36.

A well-known fluid valve assembly 34 can be retained by the pistonhousing 24 for selectively varying the fluid flow. The valve assembly 34includes a compression intake valve spring 42 mounted on the internalvalve seat 23 of the piston housing 24. An annular compression intakevalve 44 is placed adjacent the valve spring 42, followed by an orificeplate 46. A rebound valve 48 is adapted to be supported on the oppositesurface of the orifice plate 42 and controlled by a compression spring50. A valve cage 52 is compressed against the spring 50. The skirt 20 isbent or crimped inwardly over the valve cage 52 to retain the componentsof the valve assembly 34 inside the piston housing 24. A sealing band54, preferably formed from TEFLON, is retained by the grooves 22 on theouter circumference of the piston housing 24.

The piston and piston rod subassembly 30 are reciprocally mounted in theinner cylinder 56 of a hydraulic damper 58 partially illustrated in FIG.9. The inner cylinder 56 is closed at its lower end by a well-known basevalve assembly 60. A reservoir tube 62 closed at its lower end by an endcap 64 contains the inner cylinder 56. As the piston and piston rodsubassembly 30 reciprocate, fluid travels through the piston valveassembly 34 and base valve assembly 60 in a well-known manner.

The pattern of tabs 14 and 16 can be varied as needed to provide fluidopenings through the piston housing 24. For example, the lengths of theshort tabs 16 can be reduced to allow fluid to flow more easily throughthe piston housing 24. In a similar manner, the distance betweenadjacent tabs 14 and 16 can be increased to provide less restrictedfluid flow through the piston housing 24. It is appreciated that fluidpassages can be provided through the piston rod 32.

The present piston housing 24 having bendable tabs 14 and 16 provides aneconomical connection to the present flanged rod 32 without expensivethreading or the inherent problems of welding. The piston and piston rodassembly 30 can be used with known fluid valving and can be utilizedwith conventional shock absorbers and struts.

Although the present invention has been described with reference to apreferred embodiment, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method of forming apiston and piston rod assembly for use with a hydraulic damper, themethod comprising:a) forming an annular flange at one end of acylindrical piston rod; b) providing a generally flat, bendable blank;c) cutting a plurality of bendable tabs along one edge of the blank; d)forming the blank into a cylindrical body; e) inserting the piston rodinto the cylindrical body; f) bending the tabs onto the flanged end ofthe piston rod, thereby attaching the cylindrical body onto the pistonrod; g) providing a bendable annular skirt at an edge of the cylindricalbody opposite the tabs; h) inserting a valve assembly inside the body;and i) bending the skirt to retain the valve assembly inside the body.2. The method as specified in claim 1 including:a) bending a first groupof the tabs to form a seat for the piston rod flange; b) seating a lowersurface of the piston rod flange on the seat; and c) bending theremaining tabs over an upper surface of the piston rod flange, therebyretaining the housing on the piston rod.
 3. The method as specified inclaim 2 wherein the first group of tabs are shorter than the remainingtabs.
 4. The method as specified in claim 1 wherein the tabs arespaced-apart.
 5. The method as specified in claim 4 wherein clearancesbetween the tabs comprise valving means.
 6. The method as specified inclaim 1 including:a) bending a first group of the tabs radially inwardlyto form a seat for the piston rod flange; b) seating a lower surface ofpiston rod flange on the seat; and c) bending a second group of the tabsaround the piston rod flange, thereby retaining the piston body to thepiston rod.
 7. The method as specified in claim 6 wherein the firstgroups of tabs are shorter than the second group of tabs.
 8. A method offorming a piston to be mounted on a piston rod of a hydraulic damper,the method comprising:a) providing a generally flat, bendable blankhaving first and second longitudinal edges; b) cutting first and secondgroups of bendable, spaced-apart tabs along the first edge; c) formingthe blank into a cylindrical body; d) bending the first group of tabsinto a seat for receiving the piston rod; e) forming a bendable annularskirt along the second edge; f) inserting a valve assembly into thecylindrical body; and g) bending the skirt to retain the valve assemblyinside the body.
 9. The method as specified in claim 8 whereinclearances between the tabs comprise valving means.
 10. A method offorming a piston and then mounting the piston onto a flanged piston rod,the method comprising:a) providing a generally flat, bendable blankhaving first and second longitudinal edges; b) cutting first and secondgroups of bendable, spaced-apart tabs along the first edge; c) formingthe blank into a cylindrical body; d) bending the first group of tabsinto a seat for receiving the piston rod; e) forming a bendable annularskirt along the second edge; f) inserting a valve assembly into thecylindrical body; g) bending the skirt to retain the valve assemblyinside the body; h) seating the flanged piston rod on the seat formed bythe bent group of first tabs; and i) bending the second group of tabsover an upper surface of the flanged piston rod, thereby retaining thecylindrical body to the piston rod.
 11. The method as specified in claim10 wherein the first group of tabs are shorter than the second group oftabs.